This project is concerned with the development and eventual application of methodology for combining evoked potential (EP) recording with regional cerebral blood flow (rCBF) activation imaging. Positron emission tomography (PET) is now known to be a powerful method for studying localization of function during sensory, motor and cognitive task performance. However, PET is incapable of the temporal resolution necessary to study underlying physiological processes on a scale appropriate to the study of behavior, i.e., on the order tens to hundreds of milliseconds. Event related potential (ERP) recording remains the method of choice for noninvasively studying the temporal sequence of electrophysiological events which are the concomitants of behavior and cognitive task performance. A combination of PET and ERP is thus suggested as a means of studying the spatial and temporal aspects of cognitive processing together , in order to determine both sequence and location of the underlying events. Theoretical calculations and simulations are presented which define the resolution of the PET-ERP combination in both the spatial and temporal domains. Preliminary data are shown which demonstrate a reasonable correspondence between theory and practice in the visual and somatosensory systems. The assumptions which must be made in applying the combined methodology in practice are detailed together with implied limitations on the questions which can be asked. Experiments employing the PET_ERP combination which are complimentary to other subprojects in the Washington University PET laboratory are outlined for years 3-5.